Discharge door for mixers



Feb. 20, 1968 J. 5. TREMBLAY ETAL 3,369,324

DISCHARGE DOOR FOR MIXERS 4 Sheets-Sheet 1 Filed Oct. 14, 1965 J.G.T'z;a-;:2

M. B. SHAVER T. E. HARRIS 4TTORNFYS 0, 1968 J. G. TREMBLAY ETAL 3,369,324

DISCHARGE DOOR FOR MIXERS Filed Opt. 14, 1965 4 Sheets-Sheet 2 INVENTORS J. G. TREMBLAY M. B. SHAVER' T. E. HALRRIS nzzwfizz z ATTORNEYS Feb. 20, 1968 J. G. TREMBLAY ETAL 3,359,324

DISCHARGE DOOR FOR MIXEIRS 4 Sheets-Sheet 4 Filed Oct. 14, 1965 SOLD FL U/D EESERVO/R j llll i 5 m'I iiw'oks J. G. TREMBLAY M. BVSHAVER T. E. HARRIS United States Patent 3,369,324 DISCHARGE DOOR FOR MIXERS Julien G. Tremblay, Montreal, Quebec, Marvin B. Shaver, Beaconsfield, Quebec, and Thomas E. Harris, Valois, Quebec, Canada, assignors to Dominion Engineering Works Limited, Montreal, Quebec, Canada Filed Oct. 14, 1965, Ser. No. 495,984 4 Claims. (Cl. 49280) ABSTRACT OF THE DISCLOSURE The door portion of a rubber mixer is rigidly and adjustably mounted on the door support to permit accurate adjustment of the tapered sides of the door portion in mating relation with the divergent outlet from the mixing chamber.

This invention relates to batch mixers, of the type used in the production of rubber and plastics, in which various ingredients are subjected to a complete interchange by the action of bladed rotors operating at slightly different speeds and which results in the production of a homogenous plastic mass.

Batch mixers of this type are provided with mixing chambers having bottom openings through which the plastic mass is discharged on completion of the mixing cycle. During the mixing operation the bottom opening is closed by means of a tightly fitted discharge door which is so designed that it prevents the escape of particles which constitute parts of the mix. In the closed position the discharge door forms part of the mixing chamber. The door serves to retain the ingredients within the confines of the mixing chamber and also to maintain the mix within close proximity of the rotors.

Extremely high pressures are produced in the mixing chambers and numerous attempts have been made to improve the sealing and operating qualities of these discharge doors, resulting in arrangements of door operating mechanisms which fall into the following general categories; slidably mounted doors, and drop or swing doors.

This invention specifically relates to improvements in the drop or swing type of discharge door, wherein provision is made to lock the door in the closed position by means of an improved nonreversing door latch.

In a conventional mixer, embodying a drop door which incorporates self-centering features, the lower edges of the mixing chamber walls provide a bevelled opening against which a correspondingly bevelled door is fitted. The lower surface of the door is mounted on a door supporting member which is pivotally mounted and operable to effect door opening and closing movements. A rubber mat or springs are positioned between the door and the supporting member to provide for self-centering of the door against the bevelled opening. An hydraulically operated latch member holds the door in the closed position.

This type of conventional drop door embodies several inherent disadvantages, some of which are as follows:

(a) In practice the weight of the discharge door is so great that, each time the door assembly is opened, it becomes misaligned from its optimum position with respect to the supporting member, and much difliculty is experienced in obtaining the necessary seal when the door is reclosed.

(b) No provision is made to prevent the door slamming during the closing operation and consequent damage to the bevelled lips of the discharge opening frequently occurs.

(6) Latch pressure compress the rubber mat between the door and the supporting member and close the gap,

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thereby destroying the self-centering feature and enabling large forces to be exerted on the bevelled lips of the discharge opening.

(d) High fluid pressure is required in the latch hydraulic cylinder to maintain the door in the closed position against the action of occasional high pressure in the mixing chamber, which tend to force the door open. These occasionally high mixing chamber pressures are continually fluctuating and thus the sides of the discharge opening are subjected to a continually flluctuating load, due to the resultant of latch pressure and mixing chamber pressure. This situation is due primarily to the design of door latch which allows reverse action to take place.

In later conventional mixers embodying doors of this type check valves were fitted in the hydraulic circuits of the latch in an attempt to prevent latch reversal. However, due to fluid compressibility and/or air entrained in the hydraulic circuit, the latches were still subject to unwanted fiuctuation in performance.

The present invention overcomes the aforementioned disadvantages and has, as its main objects, the provision of a new and improved drop door, for a mixer of the type described, which utilizes a non-reversing door latch.

Another object of the invention is to provide a new and improved drop door, for a mixer of the type described, which embodies a slow-down valve in the door operating hydraulic circuit and thus prevents the door slamming during closing with consequent damage to the bevelled sides of the discharge opening.

Another object of the invention is to provide an improved door, for a mixer of the type described, which has improved sealing properties.

Another object of the invention is to provide an improved door in which the load on the bevelled sides f the discharge opening is less than has hitherto been possible, without sacrifice of the sealing qualities of the door.

A further object of the invention is to provide a new and improved drop door which can be more economically manufactured, than conventional doors.

Further objects and advantages of this invention will be apparent from the following detailed description and figures, in which:

FIGURE 1 is a front elevation, partly in section, of a typical batch mixer.

FIGURE 2 is a sectional view, to an enlarged scale, on line 22 of FIG. 1 looking in the direction of the arrows and embodies the features of this invention.

FIGURE 3 is a further enlarged detail of the View shown in FIG. 2. (FIG. 3 is located on the same sheet as FIG. 1.)

FIGURE 4 is a sectional view on line 4-4 of FIG. 2, looking in the direction of the arrows.

FIGURE 5 is a view on line 5-5 of FIG. 4, looking in the direction of the arrows.

FIGURES 6-8 show diagrams illustrating the theoretical considerations set forth in this invention.

FIGURE 9 is a schematic layout of the electrical circuit for latch and door operation.

FIGURE 10 is a schematic layout of the hydraulic circuit for latch and door operation.

With reference now to the drawings, wherein similar reference characters designate corresponding parts throughout the several views, and with particular reference to FIGS. 1 to 5, the mixer illustrated consists of two end frames 20 and 21, between which are mounted two sides 22 and 23. Sides 22 and 23, together with end frames 20 and 21, form a chamber 24 into which materials are fed for mixing. Co-mingling of the materials is performed by two rotors 25 and 26. The above mentioned assembly is supported on a base 27. At the lower end of mixing chamber 24 an opening 28 is provided for discharging the mixed mass.

During the mixing operation discharge opening 28 is tightly closed by a door 29. Door 29 is mounted on door support 30 and is rigidly secured thereto by a plurality of holding bolts 31. Door support 3G is rigidly attached to shaft 32 by means of a key 33. Shaft 32 is journalled in end frames 20 and 21. Adjacent to end frame 21,

. a hydraulically operated torque actuator 34 is attached to shaft 32, and functions to rotate shaft 32 and to open or close door 29 according to the direction of rotation. Door 29 and door support 39 are shown in the open position 35 as indicated by broken line in FIG. 2.

A plurality of jack screws 36 are alternately interspersed between bolts 31 throughout the length of door 29 and on either side of the door center-line. lack screws 36, or any other means of adjustment, may be located in any other location necessary to obtain adjustment of the door in any direction. Shims 37 of the required thickness and length can be added, if necessary, between the lower surface of door 29 and the upper surface of door support 3%.

It will thus be seen that with careful adjustment of shims 37, jack screws 36, and bolts 31, door 29 may be adjusted in any direction so that it will take up the necessary position to prevent leakage. Door 2% may also be slightly warped at any point throughout its length, or on either side of the door centerline, to effect adjustment and to compensate for any uneven surface wear which may be present along discharge opening lips 38 and 39. These adjustments, which can be accomplished without loss of rigidity to the door structure, ensure that a tight seal will be maintained without loss of the liner particles contained in chamber 24: said adjustments may be carried out from time to time as warranted.

A latch mechanism is provided to maintain the door assembly in the closed position during mixing and serves to prevent this assembly from opening due to the rapid increase in pressure within chamber 24 when mixing commences.

The latch mechanism consists of a latch 40 slidably fitted within latch housing 41; housing 41 is rigidly attached to base 27 by means of a plurality of adjustable bolts 42, or any other suitable attaching means.

Hydraulically actuated cylinder 43 operates a piston (not shown) which is mounted within cylinder 43 and which actuates latch 40 by means of piston rod extension 44.

The position of latch 40- can be linearly adjusted by means of a threaded portion 45, on extension 44-, and is capable of being locked in the desired position by a locknut 46.

When door 29 is closed, and hydraulic cylinder 43 is actuated, the angled tip 47 of latch 40 engages with a plurality of rollers 48, rotatably mounted on shaft 49 which is attached to door support 30.

The preferred angle of tip 47 of latch an is equal to, or less than, the angle of friction between latch 40 and latch housing 41.

Reference to FIGS. 68 show diagrams illustratin the theoretical considerations in the choice of latch tip angle.

The theory of friction for the example in FIG. 6 is given as follows: A block of weight W is resting on a flat surface S. A force P is impending a movement to the right. Opposing the block movement is a frictional force F. A normal force N is exerted by the block W on the surface S. The co-efiicient of static friction U is defined as the ratio of the maximum static frictional force F to the normal force N between the two surfaces. In mathematical form:

Fl wv As shown in FIG. 7 the forces F and N give a re- 4;. sultant force R. The forces R and N form an angle 0. Thus:

Fl tan 6- N U This angle 0 is called the angle of friction.

Now consider the latch W as shown in FIG. 8.

A force R, is exerted on the sloped plane 47 by the drop door roller 48, which force R can be split into two rectangular components N and F. The frictional force F will oppose the force F.

The angle 0, formed between R and N will also be equal to angle a, of the sloped plane 47. From previous theory:

F=UN and tan 6 5 Movement will take place only when P is larger than F. Therefore if 6:, such that F F', no movement will take place and the angle of latch tip 47 is equal to the angle of friction.

ta1 10 Z 2 i 7 if F F then tan 0=U As on decreases, and 0 decreases, the force N increases and F decreases. P will increase as N increases. Therefore it will be impossible for the door latch 40 to retract under load from the mixing chamber. The value of a, and by the same (9, is based on the practical value of U.

Example: for steel on steel, dry surfaces,

Co-efiicient of friction=.l5

As lubrication decreases the co-efficient of friction, the angle should be reduced accordingly. Thus, the preferred angle of tip 47 will be a maximum of 8 /2".

The opening and closing movements of door 29 together with latch 40 are performed hydraulically and controlled electrically. FIGURES 9 and 10 show the schematic circuit lay-outs for electrical and hydraulic components, respectively.

FIGURE 9 shows the schematic electrical circuit for the operation of the electrically operated hydraulic valves and required limit switches to provide signals for proper operating sequence. The components in this circuit will be detailed, later in this specification, during the description of combined electrical and hydraulic operations.

FIGURE 10 shows the schematic hydraulic circuit and includes a fluid reservoir 50 and a variable volume pump 51, actuated by an electric motor 52 and used to develop the fluid pressure required to actuate the piston 53 in hydraulic cylinder 43 and the torque actuator 34. The pressurized fluid circulates through a check valve 54 which serves to maintain the fluid in a pressurized condition and also prevents the fluid from draining back into reservoir 50. Part of the fluid delivered by pump 51 is directed into and is then stored in the accumulator 55 which would allow opening of mixer door 29 in the event of a power failure. Mounted in this line is a pressure switch 56 utilized to shut off motor 51 when the desired pressure is reached and to re-start motor 51 when the fluid pressure has dropped below a certain value. The pressure gauge 57 permits the reading of the fluid pressure existing in the line and also indicates the proper functioning of the fluid system. Heat exchanger 58 is incorporated to cool the fluid before it returns to reservoir 50.

Operation of the schematic circuits shows in FIGS. 9 and 10, for discharge door opening and closing sequences, is as follows:

To open the discharge door The selector switch 59 is moved to DOOR OPEN position. The green light 60, indicating DOOR.

CLOSED, is extinguished due to opening of electrical lines L1 and L2. The solenoids A, B, D, and H are deenergized. The solenoid C in four-way valve 61 is energized allowing the pressurized fluid to enter cylinder 43 on the left-hand or rod side and thus retracting door latch 40 from rollers 48. Check valve 61A permits return flow of fluid from right-hand side of piston 53. As latch 40 retracts, the limit switch 62 is released and the red light 63, indicating DOOR OPEN, is illuminated. At the end of the latch retraction stroke, the limit switch 64 is actuated, energizing solenoid B in four-way valve 65 and allowing the fluid to act at point 66, of the hydraulically operated part of four-way valve 65, to shift the valve spool to place the crossed arrows into the oil lines and to permit the fluid to pass through the volume control valve 67 and into the torque actuator 34 to open the door. Door 29 mounted on door support 30 is directly coupled to torque actuator 34. The check valve 68 allows fluid to be drawn into torque actuator 34 during the free fall of discharge door 29. Door 29 continues to open until the cam 69, on the torque actuator 34, engages the plunger on the decelerating valve 70, causing the door to slow down and stop. Valve 70 controls the final open position of the door and can also be operated manually. By turning an adjusting screw on valve 70, further door opening movement can be obtained for cleaning and maintenance. In the final door open position, the limit switch 71 is engaged to ready the circuit for its next sequence. Until limit switch 71 is engaged, the door can not be closed.

T 0 close the discharge door The selector switch 59 is moved to DOOR CLOSE position. Solenoids B and C are de-energized and A is energized, actuating four-way valve 65 and thus allowing pressurized fluid to reach point 72 which will shift the valve spool to place the parallel arrows into the oil lines. The fluid will then reach volume control valve 73 and two-way valve 74 at point 75. The fluid will pass ireely through point 75. The fluid then passes through the deceleration valve 7 0, which has a free flow in this direction, and the door starts to close. The limit switch 76, is tripped just prior to the door fully closed position, to energize the solenoid H which will let fluid enter the hydraulic differential part of valve 74 and close passage 75, and then fluid will only pass through the slow down volume control valve 73 which has a restricted flow and will slow down the closing movement of door 29 and prevent it slamming against lips 38 and 39 of opening 28. When the door is fully closed, the limit switch 77 is engaged energizing solenoid D, shifting the valve spool in valve 61, and allowing fluid to pass through the pressure reducing valve 78 and into the right-hand or piston side of cylinder 43 which will extend latch 40 to contact rollers 48 and lock the door. As latch 40 extends limit switch 64 is released, to ready the circuit for its next sequence. When latch 40 is fully extended, limit switch 62 is tripped, red light 63 is extinguished, and green light 60 is illuminated to indicate that the door is closed and the mixer is ready for loading. The pressure reducing valve 78, is used to regulate the pressure which moves the latch 40 into closed position against rollers 48 and is adjusted to ensure that suflicient pressure is exerted on the door assembly to prevent leakage of the contents in chamber 24, yet is not high enough to damage sloping lips 38 and 39 of discharge opening 28.

Latch housing 41 may be adjustably or pivotally mounted on base 27 to provide, in combination with a particular angle of latch tip 47, the required resultant angle for non-reversing operation.

Latch tip 47 has been illustrated as a single plane slope of specific angle, however it should be realized that double or multiple plane surfaces, a curved surface, or combinations thereof, could be embodied to vary the rate of action, provided that the specified effective angle is maintained for roller contact.

To summarize the present invention, we have provided means whereby a batch mixer is provided with an improved drop door, wherein the closing rate is controlled to reduce risk of damage; We have provided a new and improved door which can be adjusted by means of shims, jack screws and bolts to accommodate any misalignment or wear on the sloping lips of the discharge opening and, furthermore, we have provided a new and improved latch mechanism to securely maintain the drop door assembly in the closed position without risk of premature opening.

It will be seen from the foregoing that we have provided new and improved means for accomplishing all of the objects and advantages of the invention as set forth and that changes may be made in the details of construction without departing in any way from the spirit or scope of the invention.

What we claim is:

1. In a mixer of the type for mixing rubber or plastics, having an elongated mixing chamber, a narrow elongated dis-charge opening in the bottom of the chamber having the sides divergent in an opening sense, the improvement comprising closure means swingahly mounted beneath said discharge opening for movement to open and close the opening, having door support means rigidly attached to pivotal mounting means for rotational movement thereabout, a door member mounted on said support means, having tapered side portions substantially corresponding with said divergent discharge sides, and non-resilient mounting means in spaced relation along the length of said closure means adjustably securing said door member to said support means including a plurality of bolting means and a plurality of jacking means interspersed therebetween to provide non-resilient local adjustment to fitting surfaces of said door member relative to said discharge opening whereby sealing of said closure means is improved and undue wear of fitting surfaces is substantially precluded.

2. The mixer as claimed in claim 1 having at least one slidable latch member movable into securing relation with said closure means in the closed position, the contacting face of said latch member in contact with said closure means lying in a plane at an angle to the plane normal to the downward force acting on said closure means, said angle being approximately equal to the angle of friction between said latch member and the contacting surface supporting said latch member.

3. The mixer as claimed in claim 2 having hydraulic means for slidably operating said latch means.

4. The mixer as claimed in claim I having hydraulic means for moving said closure means to a closed position.

References Cited UNITED STATES PATENTS 2,686,497 8/1954 Dooley 49-340 2,790,493 4/ 1957 Wenzelberger 222-504 X 2,918,905 12/1959 MacLeod et al 60-52 2,939,616 6/1960 Whittum et al. 222512 2,962,186 11/ 1960 Gottschalk 220--57 3,099,438 7/ 1963 Fritz 49-280 3,135,440 6/1964 Baran 49340 X DAVID J. WILLIAMOWSKY, Primary Eramincr. I. KARL BELL, Assistant Examiner. 

